1. Field of the Invention
The invention relates to radioactive therapeutic seeds. More particularly, the invention relates to improved radioactive therapeutic seeds for the treatment of oncological and other medical conditions.
2. State of the Art
Radioactive seed therapy is a well known and well accepted medical procedure for the treatment of various oncological and other medical conditions. Seed therapy, also known as brachytherapy typically involves the implantation of one or more tiny capsules (seeds) into or around a treatment site. The capsules contain a radioactive isotope that irradiates the treatment site at close range without adversely affecting other parts of the body. Brachytherapy has been used successfully in the treatment of various types of cancers such as prostate cancer. It has also been used to prevent the growth or regrowth of tissues in the treatment of various occlusive diseases such as arteriosclerosis and arthrosclerosis subsequent to balloon angioplasty.
Radioactive therapeutic seeds are carefully designed to possess several important qualities. First, they are relatively small, typically approximately 0.025 inch in diameter and approximately 0.16 inch long, so that they may be implanted using minimally invasive instruments and techniques. Second, the radioactive isotope must be enclosed in a biocompatible protective package since the seeds are typically not removed and will remain in the body for many years. Third, the isotope should be positioned within the protective package so as to avoid any "hot spots" of radiation. Fourth, each seed preferably includes a radiopaque (e.g. high Z material) marker so that it can be located at the treatment site with the aid of fluoroscopy. Fifth, the protective package and the radiopaque marker are preferably configured such that each does not cast "shadows" in the irradiation pattern of the isotope.
The state of the art of radioactive therapeutic seeds is substantially disclosed in seven U.S. patents: U.S. Pat. No. 5,713,828 to Coiglione for "Hollow-Tube Brachytherapy Device", U.S. Pat. No. 5,405,309 to Carden, Jr. for "X-Ray Emitting Interstitial Implants", U.S. Pat. No. 4,891,165 to Suthanthiran for "Device and Method for Encapsulating Radioactive Materials" and U.S. Pat. No. 4,784,116 to Russell, Jr. et al. for "Capsule for Interstitial Implants", U.S. Pat. No. 4,702,228 to Russell, Jr. et al. for "X-Ray Emitting Interstitial Implants", U.S. Pat. No. 4,323,055 to Kubiatowicz for "Radioactive Iodine Seed", and U.S. Pat. No. 3,351,049 to Lawrence for "Therapeutic Metal Seed Containing within a Radioactive Isotope Disposed on a Carrier and Method of Manufacture".
The Lawrence patent describes many of the essential features of radioactive therapeutic seeds. Lawrence describes radioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) which emit low energy X-rays and which have relatively short half-lives. Once implanted at a treatment site, these isotopes provide sufficient radiotherapy without posing a radiation danger to the medical practitioner(s), people in the vicinity of the patient, or other parts of the patient's body. Lawrence further describes a protective capsule which contains the isotope and prevents it from migrating throughout the body where it might interfere with healthy tissue. The capsule is cylindrical and made of low atomic number biocompatible materials such as stainless steel or titanium which substantially do not absorb X-rays. The isotope is coated on a rod shaped carrier made of similar X-ray transparent (e.g. low Z) material and is placed inside the capsule cylinder. The ends of the capsule cylinder are closed by swaging or spinning and soldering or welding. According to a preferred embodiment, Lawrence places a radiopaque marker inside the seed. In one embodiment, the marker is a wire embedded inside the carrier rod. The wire is made of high atomic number material such as gold or tungsten which absorb X-rays.
Kubiatowicz made a minor improvement in the basic Lawrence design by providing that the entire isotope carrier be made of radiopaque material such as silver. Kubiatowicz recognized that since the isotope was carried on the entire outer surface of the carrier, there was no need to make the carrier body X-ray transparent as suggested by Lawrence. The larger radiopaque carrier body described by Kubiatowicz makes the seeds easier to see with X-ray or fluoroscopic examination. Thus, the seeds may be placed more accurately at or around the treatment site.
The Coniglione patent provided a tubular seed adapted for longitudinally receiving suture material to facilitate securing the seed at an implant site. The seed optionally includes a radiopaque band centrally located on the outer surface of the seed, and the radioactive isotope either extends over the entire outer surface of the seed, including over the band, or is coated on the outer surface of the seed from the ends of the seed to areas adjacent the edges of the band.
Despite the fact that radioactive therapeutic seeds have been in use for over thirty years and despite the several significant improvements made in these seeds, many concerns still exist regarding their design. In certain instances where radioactive seed therapy is prescribed for a patient, a physician may desire to have different levels of radioactivity at various locations within the treatment site and thereafter monitor how the tissue is affected by seeds radiating particular levels of radiation. Or the physician may want to implant seeds having isotopes with to different half lives, thereby permitting selected locations to receive radiation over a longer period of time, and monitor which seeds are active. However, according to the known seed designs and methodology, it is not possible to distinguish one seed from another after implantation based upon a seed marker with an imaging systems, e.g., X-ray. Due to the indistinguishability of the seeds, implantation of seeds having different respective properties at a single site of treatment is not purposefully performed.